BAGHDAD Islamic State's deadliest attacks for months in and around Baghdad could be a sign that Iraqi forces are stretched thin after recent advances to reclaim territory from the group, according to some military commanders and a provincial official.

Iraqi forces backed by air strikes from a U.S.-led coalition retook the northern city of Baiji in October and then Ramadi, 100 km (60 miles) west of Baghdad, at the end of last year.

But the government's determination to move on the militant stronghold of Mosul in the far north this year has prevented the military from consolidating gains on the northern and eastern outskirts of Ramadi, said the commanders.

They said this has allowed Islamic State fighters to regroup and continue sending weapons from deep inside the "caliphate" to Falluja and Garma - areas just west of Baghdad where security officials said Sunday's attacks were launched from.

A twin suicide bombing in the Sadr City district of Baghdad killed 78 people. Islamic State also said it was behind an assault on police and army positions in the western outskirts of Abu Ghraib, which killed 24 security forces and gave the insurgents control of the country's largest grain silo for most of the day.

Iraqi officials and a spokesman for the U.S.-led coalition said the Baghdad attacks were aimed primarily at boosting the militants' morale after losing ground in Ramadi two months ago.

But the attacks have raised questions about security in the capital, home to four million people, and the government's ability to move on Mosul this year without letting other reclaimed areas fall back under the group's control.

The closest Islamic State position to Baghdad - which has never been under the group's control - is Falluja, 50 km to the west, which Iraqi forces have been encircling for months. Sunday's attackers were able to breach the military's defences there and in the adjacent area of Garma, officials said.

Two Iraqi army officers stationed near Ramadi told Reuters that a shortage of troops had slowed the military's advance to a crawl in the city's northern and eastern outskirts.

Most of the elite counter-terrorism forces that spearheaded the city's capture have been redeployed elsewhere and replaced by less effective army and police units.

"After the seizure of Ramadi, military operations have abated. That was a tactical mistake as Daesh fighters were given the chance to take a breath and regroup," said a colonel from the ninth division, using an Arabic acronym for Islamic State.

"We need more reinforcements to fill the gap left by the counter-terrorism forces if we want to keep the momentum high."

The colonel also criticised the government's decision to mobilise hundreds of troops this month to Makhmour, a base south of Mosul.

"Every single soldier is needed to drive the remaining pockets of Daesh from rural areas around Ramadi," he said by phone. "This is what I call blundering army tactics."

Fadhil Abu Ragheef, a Baghdad-based security analyst, said a nine-month offensive in Garma by Iraqi forces "had not achieved any victory worth mentioning", leaving Islamic State militants there the space to launch the Abu Ghraib attack.

PROTECTING BAGHDAD

Iraqi military spokesman Brigadier General Yahya Rasool said Iraq had sufficient forces for operations on multiple fronts.

"We won't neglect anything," he told Reuters. "Everything is planned. There is the joint operations command and a planning committee that includes highly competent senior officers and we are working on the plans."

Yet according to Falih al-Essawi, deputy head of the provincial council of Anbar where Ramadi and Falluja are located, the Abu Ghraib attack should be a "red flag" to the government to review security in the capital.

"When Daesh fighters control an area that is a 15-minute drive from Baghdad, that means there are serious security flaws that need to be addressed," he said.

Islamic State threatened to overrun Baghdad 20 months ago during its advance through northern and western areas after crossing the Syrian border but the capital has since seen relative calm.

The authorities said this month they were reorganising checkpoints and closing gaps in the perimeter around Baghdad in a bid to prevent further militant attacks.

In the Abu Ghraib attack, the militants infiltrated the city from Garma and Falluja using all-terrain vehicles so they could use dirt roads to evade detection by Iraqi forces, security officials said.

Security forces mostly regained control of Abu Ghraib by Sunday evening, including a grain silo and a cemetery where Islamic State had dug in for hours.

Essawi and a trade ministry official suggested the attack was partly motivated by Islamic State's desire to seize wheat stored in the silo to feed residents in the encircled areas of Falluja and Garma, but said the militants had not managed to take the supplies before fleeing.

SLEEPER CELLS

Army Lieutenant Colonel Fadhil al-Mohammadawi said the military was still pursuing militants on Monday in rural areas of Abu Ghraib and checking for sleeper cells suspected of participating in the attacks.

Two witnesses said on Monday that Islamic State paraded the bodies of 12 Iraqi soldiers through the streets of Garma in the back of a pickup truck. Images distributed online by Islamic State supporters showed several bodies clad in military uniforms in the back of a muddy white pickup truck, along with Humvees and army trucks allegedly seized in Sunday's attacks.

Reuters could not verify the authenticity of the photos or the witness accounts.

Coalition spokesman U.S. Army Colonel Christopher Garver said local commanders were right to be concerned about holding territory recently recovered from Islamic State but added that planning already takes such concerns into consideration.

The coalition has so far trained about 2,000 Anbar police to be the main holding force in Ramadi, he added.

Graver said the formation that attacked Abu Ghraib was not "particularly large" and showed that the coalition and the Iraqis were succeeding in preventing Islamic State from conducting major resupply and manoeuvring.

"You'll never be able to get the noose so tight that a well-trained person can't move in and out of the area," he said, but the Iraqi military "now stands its ground and even if they were to tactically fall back as we've seen a couple times, they retake the ground".

Graver said it was up to the Iraqi government to decide how best to mobilise its limited resources to advance towards Mosul.

"You don't want to just pick up and move everything because you don't want to give back the ground that you just took, and so far we haven't seen that."